Schematics / CV Twister-Wave Warper Adaptation
CV Twister / Wave Warper adaptation by Grant Richter . From the description on the site http://www.musicsynthesizer.com/diy/grant/CVtwister2.html :
This is a circuit adapted from the Sandin Image Processor. The original circuit was used to give "solarized" effects to video signals.
With some redesign it also makes a nice low parts count control voltage twister / wave warper circuit for audio. The bandwidth is limited by the op-amp type, and should extend above 20 Khz with this design.
The basic idea is to use diodes to split the input voltage into three sections - plus, minus and "near zero". Each section is then run to a scalable follow/invert circuit. Since the breakpoints are fixed by the diode voltage drop, an input "span" control allows adjustment of the breakpoint relative to the input voltage range. The output "Gain" control then allows boosting the signal back up to the 10 volt range. The sections could also be 3/4 of a quad op-amp. The 5.1K resistors and 10K pots could also be 47K or 51K and the pots 100K. The higher current of the 10K makes the breakpoints a little sharper, but it should still work with the higher resistances.